Studies of adults with alcohol dependence indicate a close relation between sleep disturbances and alcohol use and abuse. Few studies have examined these relations in young humans; fewer have examined the role of the circadian timing or sleep/wake homeostatic systems in alcohol utilization and metabolism; and none has attempted to determine association of family history of alcoholism with sleep of offspring. This project includes three studies aimed at assessing these associations. Study 1 provides the first attempt to examine sleep patterns, sleep architecture, and a marker of the circadian timing system (melatonin onset phase) in children ages 9 and 10, adolescents ages 15 and 16, and young adults ages 21 and 22 with (PH+) or without (PH-) parental history of alcohol abuse/dependence (N = 200). A subset of older participants have moderate to high prior experience with alcohol (etoh+). We will test hypotheses that sleep is more disturbed in (1) PH+ participants, (2) etoh+ participants, (3) and in older participants at an initial assessment. We also predict that participants with both PH+ and etoh+ will show most disruption. A 2.5-yr longitudinal component in a subgroup of 80 low alcohol-experience children and adolescents will test the hypotheses that (1) pre-existing sleep disruptions predict amount of alcohol use in the 2.5-year follow up and (2) alcohol use during follow-up predicts changes in sleep between the initial and the 2.5- year in-lab assessments. In Study 2, effects of a moderate evening dose of alcohol on sleep, waking performance, and circadian phase will be studied in 64 adolescents and young adults with low alcohol exposure and PH+ or PH-. We will test the hypothesis that alcohol will alter sleep architecture and waking performance in predictable ways and that the effects will be blunted in PH+ offspring relative to PH- offspring. Additionally, we will assess whether alcohol- induced alterations in SWS are associated with slope of the decline in core body temperature following alcohol ingestion. Study 3 uses the forced desynchrony paradigm, in which participants will live in the laboratory for nearly weeks on a 20-hour day, to determine the independent and interactive contributions of the circadian timing system and sleep/wake homeostatic processes to the effects of moderate doses of alcohol on sleep, sleepiness, and waking performance. Study 3 involves a total of 24 FH- participants.